Anaerobic Digestion - PowerPoint Presentation

Slide1

Anaerobic Digestionfor Organic Waste Treatment

Rami E. Kremesti M.Sc., CWEM, CSci, CEnvSlide2

HistoryAncient technologyFirst Anaerobic Digestion plant in Bombay in 1859

In 1895 Methane produced by AD was used to light street lamps in Exeter, EnglandSlide3

IntroductionAnaerobic digestion (AD) is the method of organic wastes treatment aimed at decomposition of complex organic substances into simple, chemically stabilized compounds, mainly methane and CO

2 and digestate (biofertilizer a.k.a

Compost).

This conversion of complex organic compounds to methane and CO

2

is possible due to the cooperation of four different groups of microorganisms: fermentative, syntrophic,

acetogenic

, and methanogenic bacteria.

The main process steps of anaerobic digestion of organic wastes are: hydrolysis, acid formation,

acetogenesis

, and methanogenesis.

Microbes adopt various pathways to evade the unfavourable conditions in the anaerobic digester like competition between sulphate reducing bacteria (SRB) and methane forming bacteria for the same substrate. Slide4

AD Compared to Aerobic WW Treatment

Disadvantage of AD compared to Aerobic Biodegradation is that the start up time of an AD reactor can be up to 3 months compared to 2 weeks for aerobic reactor. Slide5

HydrolysisDuring hydrolysis of the polymerized, mostly insoluble organic compounds, like carbohydrates, proteins and fats, these large molecules are decomposed into soluble monomers and dimers, that is, monosaccharides, amino acids, fatty acids and alcohols.

This is accomplished through enzymes from the group of hydrolases (amylases, proteases, and lipases) produced by appropriate strains of hydrolytic bacteria.Hydrolysis is carried out by bacteria from the group of relative anaerobes of genera like Streptococcus and

Entero

bacteriumSlide6

AcidogenesisDuring this stage, acidifying bacteria convert water-soluble chemical substances, including hydrolysis products, to short-chain organic acids (formic, acetic, propionic, butyric, and

pentanoic), amino acids and peptides, alcohols (methanol, ethanol), aldehydes, carbon dioxide, and hydrogen.Among the by-products of acidogenesis

, ammonia and hydrogen sulphide by-products give an intense unpleasant smell to this phase of the process.

The acid phase bacteria belonging to facultative anaerobes use oxygen accidentally introduced into the process, creating favourable conditions for the development of obligatory anaerobes of the following genera: Pseudomonas, Bacillus, Clostridium, Micrococcus, or

Flavobacterium

.Slide7

AcetogenesisIn this process, the acetate bacteria including those of the genera of Syntrophomonas

and Syntrophobacter convert the acid phase products into acetates and hydrogen which may be used by methanogenic bacteria. As a result of

acetogenesis

, hydrogen is released, which exhibits toxic effects on the microorganisms which carry out this process. Therefore, a symbiosis is necessary for

acetogenic

bacteria with autotrophic methane bacteria using hydrogen, hereinafter referred to as

syntrophy

Acetogenesis

is a phase which determines the efficiency of biogas production, because approximately 70% of methane arises from the process of acetate reduction.Slide8

MethanogenesisIn this phase the production of methane by methanogenic bacteria occurs.Methanogens as absolutely anaerobic microorganisms inhabit anaerobic environment ecosystems, such as

tundras, marshlands, rice fields, bottom deposit, swamps, sandy lagoons, tanks where wastewater is decomposed, sewage sludge, solid wastes landfills, and ruminants’ stomachs (in the rumen).

These microorganisms are particularly sensitive to changes in temperature and pH, and their development is inhibited by high levels of volatile fatty acids and other compounds, such as hydrogen, ammonia, and H

2

S in the environment

Among methanogenic microorganisms, we can distinguish

psychro

-,

meso

- (35 °C) and thermophilic microorganisms

(55 °C).

The methanogenic Archaea are responsible for the final and critical step of anaerobic digestion, as they produce valuable methane.Slide9

Methanogenic Pathways

The SAB consist mostly of Clostridium sp. at both mesophilic and thermophilic conditions.

The

hydrogenotrophic

methanogens in both mesophilic and thermophilic anaerobic

digesters belong to the two orders of

Methanobacteriales

and

MethanomicrobialesSlide10

Factors Influencing ADRetention TimepH

C:N RatioMixingTemperatureF/M Ratio or Organic Loading Rate (OLR)Alkalinity

Trace Metals (Micronutrients)

Concentration of Sulphate (SRB’s favouring)

PollutantsSlide11

Technologically Five Process StagesPre-treatmentAnaerobic DigestionGas Treatment (scrubbing H

2S and CO2)Digestate treatment (sterilization) - Dewatering

Supernatant Aerobic/ANNAMOX Treatment (digester supernatant is high in P and Ammonia-N)Slide12

Large AD Vertical Reactor Schematic (Municipal AD)Slide13

Large Egg Shaped Digesters (Municipal)Slide14

A Plug Flow AD Horizontal Reactor for FarmsSlide15

Photo of Farm Horizontal AD – 750 kWSlide16

Types of DigestersFive main types of Anaerobic Digesters: Complete Stir Tank Reactor, Plug-Flow, Packed Bed Biofilm AD, Covered AD Lagoon, UASB

(upflow anaerobic granules sludge bed reactor)

Excellent e-Learning Video on Types of Anaerobic Digesters:

https://www.youtube.com/watch?v=u_ArD9jemaE

Slide17

Upflow (Granular) Anaerobic Sludge Blanket Process - UASB

Developed in Holland by Dr.

Gatze

Lettinga

in the 1970s

High Rate

Positive Energy Footprint

Low sludge production

Popular - 72

% of all

AD plants are based on UASB

Up to 90% Removal efficiency of Biodegradable COD

Up flow encourages formation of heavier granules and washes out suspended bacteria

The four top applications of high rate anaerobic reactor systems are for:

Breweries

and beverage industry

Distilleries and fermentation industry

Food Industry

Pulp and paper.Slide18

Granular Anaerobic SludgeSlide19

AD Sludge Granule StructureSlide20

Biogas Scrubbing and DryingWater vapor in biogas needs to be removed usually by condensing on cold surfaceH2S in biogas is corrosive to engines and needs to be removed in caustic scrubber

CO2 can also removed in the same processProduct is nearly pure CH4 (methane)Slide21

Biogas StorageSlide22

Video of Anaerobic Digester Operation On Dairy FarmAnaerobic Digester - Bellingham Technical College

https://www.youtube.com/watch?v=7LPfno2KPcg Slide23

Suppliers of AD TechnologyMarches Biogas (http://marchesbiogas.com for farms - UK)

DVO Inc USA (http://www.dvoinc.com for farms - USA)Bioconstruct Germany (

http://www.bioconstruct.com/

for farms)

OVIVO Water UK – AD for Municipals WWTWs (

http://www.ovivowater.com/

)

Waterleau

Belgium (

http://www.waterleau.com

) AD

Degremont

(

http://www.degremont-industry.com/

) for Municipal ADSlide24

Referenceshttp://erefdn.org/images/uploads/Griffin_Laura.pdf

http://www.hindawi.com/journals/tswj/2014/183752/ Water Wikihttp://

www.slideshare.net/sakiliubat/uasb-water-treatment-process

http://www.slideshare.net/zakiabedeen/anaerobic-aerobic-digestion

http://www.sswm.info